In conveyor belt systems, there generally is provided a continuous loop belt which is trained over opposite end rollers and intermediate support rollers. The belt is generally of a flat rectangular cross-section and has an extended length, and the ends of the belt are connected together in any of several ways to form the loop. For example, there are vulcanizing techniques which provide a virtually hidden joint having exterior surfaces smooth and flush with the belt surfaces; and there are mechanical fasteners which can be attached to butted opposite belt ends to hold them together. The belt itself generally includes a carcass having a woven or stranded inner casing and opposite upper and lower overlays or coatings of rubber or other flexible impervious material that protects the casing from abrasion, corrosion or the like. The formation of undercuts or grooves in the upper and lower surfaces of the belt to receive the mechanical fasteners has been a considerable problem. The depth of the undercut should be substantially uniform and the width should be relatively constant. The rubber, synthetic rubber or elastomeric material resists cutting with conventional cutters. Often the cutting must be done at the conveyor site where the belt has broken. In such instances, electrical power may not be readily available and it is not possible to cart large machines or apparatus to the belt ends to form the cuts. Thus, there is a need for a portable apparatus which will form the desired undercuts in such belts and is often in very adverse environments with only manual force available to make the undercut.